This invention concerns manufacture of welding rod or wire suitable for use as in Metallic Inert Gas (MIG) or Tungsten Inert Gas (TIG) welding and more particularly manufacture of steel or iron welding rod or wire. A problem has existed in the manufacture and supply of ferrous welding rod or wire in that the rod surface will, over a period of time under normal shelf conditions, develop surface formations of red oxide of iron. Such oxidation renders the welding rod unmarketable due to its appearance. If heavy oxidation occurs, the rod will be unsuitable for use due to the effect of such red oxide on the welds. The deoxidizers such as silicon and manganese normally present in the weld rod composition cannot effectively eliminate relatively large masses of red oxide, resulting in the includes thereof in the resultant weld. Also, this oxidation may interfere with proper operation of the welding rod feed equipment utilized in automated welding operations, due to the roughening of the surface and the change in diameter due to the presence of relatively gross red oxide formations. Relatively thick patches of red oxide can also prevent good electrical contact, interfering with proper functioning of arc welding equipment.
For this reason, attempts have long been made to treat the surface of the welding rod such as to increase its corrosion resistance. Such treatments have in the past included plating or coating of the wire with corrosion resistant metals. Copper plating has in the past and is currently being used for such application, which affords a degree of corrosion resistance. This approach has the disadvantage of high cost, since the process (copper phosphating) is costly and copper metal prices are often high. The copper also has a tendency to accumulate if the welded material is salvaged from welded structures which have been fabricated with the use of such copper plated welding material. If excessive amounts of copper are contained in the weld, a certain degree of embrittlement may occur. These problems are also inherent in plating the welding rod or wire with other metals such as zinc or silver.
Welding rod or wire is commonly employed in automated operations in which a feed reel mechanism causes the welding rod or wire to be advanced to the site of the weld automatically and such automated operations the feedrate of the rod or wire must be very closely controlled in order to produce acceptable weld seams. Any variations in the diameter of such welding rod or wire generally causes problems in providing proper feed, as can the surface roughness.
Accordingly, any such treatment of the welding rod must not interfere with the quality of the weld formed with the use of such rod; it should not appreciably affect the diameter of the rod such that its final finished diameter may be carefully controlled; the resultant surface finish should not result in poor electrical contact for MIG welding applications. At the same time this treatment should provide a high degree of corrosion resistance for the purposes outlined above.
U.S. Pat. No. 3,870,854 to Vandenbroucke discloses a treatment which is intended to solve the corrosion problem. The treatment consists of a heat treat or furnace generated black oxide surface coating of the welding rod or wire, achieved by placing the welding rod after the primary manufacturing steps, into an annealing oven and holding such welding rod at relatively elevated temperatures to encourage the formation of black iron oxide. As disclosed in that patent, the resultant very thin black oxide coating does not appreciably affect the diameter of the welding rod and in addition the black oxide material provides a relatively smooth uninterrupted surface which does not interfere with the feed and/or the electrical connection necessary for arc welding applications. The treatment yields an extremely thin coating of black oxide, i.e., the patent specification describes a coating of less than 3 millimicrons thickness.
There are several disadvantages to this approach: This extremely thin layer cannot provide a high degree of corrosion resistance, albeit some improvement over untreated metal is possible. The annealing operation constitutes a relatively time consuming manufacturing step and also produces a heat induced hardening of the outer surface of the layer, creating a relatively brittle outermost layer. This brittleness creates a tendency to produce cracking of the protective layer and lessening the protection afforded.
Accordingly, it is an object of the present invention to provide a surface treatment for ferrous welding rod or wire resulting in a high degree of corrosion resistance to thereby greatly extend the shelf life of the welding rod or wire.
It is another object of the present invention to provide such surface treatment which does not appreciably affect the diameter of the welding rod or wire.
It is still another object of the present invention to provide such surface treatment in which the resultant weld produced by such treated welding rod or wire is unaffected such as to enable high quality welds to be produced while affording the corrosion resistance protection.
It is yet another object of the present invention to provide such treatment of welding rod in which the cost of manufacturing such welding rod is not substantially increased.
A further object is to provide such protection while not interfering with good electrical contact for arc welding applications.